Solar radiation includes ultraviolet (UV) radiation wavelength of which is between 200 nm and 400 nm. Exposure of skin to UV-A (320 to 400 nm) and UV-B (290 to 320 nm) radiation causes various problems like reddening of the skin, localized irritation, sunburn, melanoma and formation of wrinkles. UV radiation is also known to cause damage to hair. Therefore, it is desirable to protect the skin and other keratinous substrates of the human body from the harmful effects of both UV-A and UV-B radiation.
Cosmetic compositions comprising sunscreen agents are used to protect the skin against UV radiation. Sunscreen agents are generally classified as organic sunscreens and inorganic sunscreens.
Inorganic sunscreens are generally inorganic particles which provide protection to the skin by way of blocking the solar radiation. Examples of such sunscreens are zinc oxide and titanium dioxide. Problem with using inorganic sunscreens is that they cannot be used at high concentrations since they give an unnatural whiteness to the skin on which they are applied.
Organic sunscreens are organic compounds which act by absorbing the solar radiation at a particular range of wavelength and emitting them at a different wavelength. Organic sunscreens are classified into UV-A sunscreens and UV-B sunscreens, depending on the wavelength range over which they offer protection. The most commonly used UV-A sunscreen is of the dibenzoylmethane class. UV-B organic sunscreens from the class of cinnamic acid, salicylic acid, and diphenyl acrylic acid are well known and used in sunscreen compositions. In order to have sunscreen protection over a wide range of wavelengths, sunscreen compositions generally include both a UV-A sunscreen and a UV-B sunscreen. Problem with including both a UV-A sunscreen and a UV-B sunscreen is that firstly including both of these makes the composition expensive. UV-A sunscreens are sometimes not very stable in use, especially in the presence of UV-B sunscreens. Further they cannot be included in high concentrations since they have inherent safety and stability issues when used at these high levels.
In order to overcome this, sunscreen molecules where both UV-A and/or UV-B sunscreens have been attached to a silicone backbone to get broad spectrum protection have been reported.
U.S. Pat. No. 4,999,186A (P&G, 1987) relates to novel sunscreen agent which has the ability to absorb both UVA and UVB wavelength radiation and to compositions and methods of providing sunscreen benefits using these agents. The sunscreen agents comprise a specific type of UVA-absorbing chromophore covalently bonded to a specific type of UVB-absorbing chromophore.
JP63135324A (Nisshin Oil Mills, 1996) discloses a cinnamic acid ester compound of cholesterol as an active ingredient, having antiinflammatory action effective to sunlight dermatitis and especially having much effect for inhibiting and preventing erythema and inflammation by light of ultraviolet area in sunlight rays.
It is thus an object of the present invention to provide for a sunscreen molecule that exhibits protection against a wide range of ultraviolet radiation wavelength.
It is another object of the present invention to provide for a broad spectrum sunscreen molecule that is stable for many hours after exposure to sunlight.
By way of the present invention, a UV-A sunscreen and a UV-B sunscreen are attached to a bile acid (e.g. cholic acid) backbone which exhibits very broad spectrum UV-sunscreen efficacy while being more stable than known heretofore. The present invention is an improvement over the known art since better sun screening efficacy is obtained while having higher stability over time.